1. Field of the Invention.
The present invention relates generally to the fabrication of spindle motors used primarily in disc drives and, more particularly, to the use of a flexible printed circuit in the construction of an enclosed spindle motor.
2. Prior Art.
Disc drives are a common means of providing secondary storage in computer systems. Disc drives generally consist of a plurality of vertically aligned magnetic media discs that store data thereon. Over the surface of each disc, a read/write head provides access to the stored data. In a typical access, the head is positioned by a motor some radially distance from the center of the disc. The discs are caused to rotate underneath the head; thereby giving access to the entire circumference of the disc.
The rotation of the discs is usually accomplished by way of a spindle motor. Spindle motors generally consist of a stator assembly defined by a number of poles radiating perpendicularly out from a shaft. Conducting wire is wound around each pole to provide the necessary electromotive force to the motor when the correct current is applied. In a three phased, nine-pole spindle motor, three separate wires are wound around the stator poles--one wire for three poles of the stator.
Spindle motors may be placed into two broad categories: enclosed or cantilever/hub type spindle motors. In an enclosed spindle motor, a separate housing covers the stator assembly and defines an opening for the shaft to rise out of the housing. By comparison, a cantilever/hub type motor is not totally enclosed. Instead, the stator assembly is partially exposed to view.
Wiring a spindle motor is typically a two-step process: first, the coil wires are wound around the poles, leaving a start and finish end to each wire; the ends of which are usually soldered to lead wires. These lead wires are then routed away from the stator to be electrically mated to outside circuitry., Typically, the winding of the coil wire is an automated process. In a 9-pole, 3-phase spindle motor, one continuous length of wire is wrapped around three adjacent poles by a dedicated winding machine. This dedicated machine leaves the ends of the windings at various, predetermined angular displacements around the stator.
The mating and routing of lead wires is usually a manual process. Lead wires are manually soldering to the winding ends. Once soldered, the lead wires are manually routed out of the stator assembly to become electrically connected to outside circuitry. Outside circuitry typically controls the current flow through the windings to produce the proper phase relations.
The manner in which lead wires are routed differs depending on whether the spindle motor is an enclosed or a cantilever/hub type motor. For a cantilever/hub type spindle motor, the task of routing is less difficult. Because the stator assembly is not fully enclosed, the lead wires may be routed from the various angular displacement after the automated winding process. As discussed further below, flexible printed circuit have been used to provide electrical connection between the lead wires and outside circuitry in cantilever/hub type motors.
For enclosed spindle motors, lead wire routing is more involved. Since the stator assembly is enclosed in a housing, the lead wires are typically brought together at one given angular position around the stator and lead up along the shaft through the opening of the housing. Once outside the housing, the lead wires are then soldered to outside circuitry.
Several problems are introduced by the manual routing of enclosed spindle motors. First, the manual process is labor intensive and adds to the cost of manufacture of enclosed spindle motors. Savings could be realized if the soldering and routing could either be automated or simplified.
Second, the manual routing of lead wires to a common angular position adds some error to the control of the motor. The dedicated winding machine provides a standard number of windings per pole, typically 30 such windings. Routing extra lead wires around stator creates a resistance imbalance because the length of the different lead wires varies. This resistance imbalance creates an imbalance in the phase relations for the motor; and hence, in the angular velocity of the motor. Ultimately, the storage density of the discs is decreased because variations in the angular velocity of the motor drive may overload the capacity of the head to read or write data.
It is the object of the present invention to provide a means to eliminate the need for manually routing the ends of the windings to lead wires.
It is a further object to eliminate the need for manual solder joints involved in the soldering of winding ends to the lead wires and in the soldering the lead wires to an outside circuit.
It is yet a further object to decrease the error due to phased resistance imbalance that introduced by manual routing.